1. Field of the Invention
The present invention relates to an electron exposure device used in fine patterning by a scanning probe microscope, and to a device using this structure to evaluate electric characteristics.
2. Description of the Related Art
As the integration density of semiconductor device components increases, fine patterning technology becomes increasingly necessary, but it is expected that technology using photolithography will be limited to minimum feature dimensions of the order of 100 nm, depending on the light wavelengths and lens materials employed. In recent years, as one potential alternative system, a lithography device using a scanning probe microscope, which has been disclosed in JP-A-73906/1999 by the present inventors and in other documents, has been suggested. This type of technology, which performs exposure by exposing a resist layer applied on a substrate to an electron beam while applying a voltage between a scanning probe and the substrate, can achieve higher resolution and feature sizes on the order of 10 nm. Furthermore, as shown in Characteristics of scanning-probe lithography with a current-controlled exposure system by M. Ishibashi et al., Appl. Phys. Lett. 72(13) 30 Mar. 1998 pp. 1581-1583, a device that can keep the exposure current constant by increasing and decreasing the voltage applied has been developed to provide pattern writing with higher reproducibility.
To expose resist patterns with high resolution and stability, feedback processing under closed-loop control for regulating the exposure current to keep it constant, as mentioned above, is indispensable. There is always stray capacitance between a scanning probe and a substrate, however; therefore, if the voltage applied is changed to respond to changes in current setting values and the film thickness of the resist, charge or discharge current flows to or from the stray capacitance in addition to the exposure current that actually flows in the resist, interfering with the change in voltage. Therefore, it takes much longer for the exposure current to reach the desired value, and it is virtually impossible to expose complicated patterns requiring frequent repetitive on/off switching of the current.
The present invention focuses on the fact that, when an alternating-current (AC) voltage is applied between a probe and substrate, even if the amplitude is changed, the voltage operates so that charge or discharge current flowing to and from the stray capacitance averages out to zero over time. More specifically, if an AC voltage is used as the applied voltage for exposing the pattern, the charge or discharge current flowing to or from the stray capacitance becomes an alternating current. Since the current-voltage characteristic of the resist layer is not linear and current does not flow therein unless the voltage exceeds a threshold, if the amplitude center of the AC voltage is set to a value in the vicinity of the threshold, exposure current flows through the resist layer only on either the positive or negative side of the AC waveform. Therefore, if the detected current flowing in the resist layer is averaged over time using a filter, the charge or discharge current offset becomes zero, whereby only the value of the exposure current to which the resist is actually exposed can be measured. If the detected exposure current is controlled by feedback so as to be kept constant while the amplitude of the applied AC voltage is changed, it is possible to control the value of the exposure current without having this value be affected by the stray capacitance in the resist layer and accordingly to expose patterns faster.